Opto-electric/hydraulic servocactuation

ABSTRACT

A method for optical signaling for electrical switch control, and in addition, optical powering of the electrohydraulic servovalve by means of opto-electric conversion using solar cells with a battery backup and dual redundancy for reliability. Optical power sources are e.g., laser diode, LED, or high intensity lamp.

This application is a continuation of application Ser. No. 08/724,320,filed Oct. 1, 1996, now abandoned, which is a continuation ofapplication Ser. No. 08/310,959, filed Sep. 23, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to aircraft fiber-optic control systems, and inparticular to opto-electric/hydraulic servoactuation.

2. Background Art

Aircraft and aerospace vehicle flight operation depend on the correctoperation of flight control surfaces. The flight control surfaces ofpresent advanced vehicles are operated by Fly-By-Wire (FBW) hydraulicactuators, where digital/analog electronic controls provide the controlsignals for the electrohydraulic actuators.

The flight control actuators are usually located in aircraft where theyare sensitive to generic failures from EMI, EMP, RFP and lightningthreats due to type of vehicle-structural materials used or lack ofprotection incorporated. The FBW actuation technology is well developed,and has been successfully used in certain high performance aircraft forflight control actuation. Excellent performance, reliability andmaintainability have been achieved, but the system has a weakness; thatof, sensitivity to generic-environmental failures. This problem can besolved or minimized through protection, such as shielding with heavyweight penalties.

In contrast, the present invention offers another solution through theusage of fiber-optic technology, called Fly-By-Light (FBL) signaling.The FBL signal transmission is immune to these generic failures. Thisnew emerging technology can provide the proper signal transmission foractuation, which can be comparable to FBW signaling with respect toperformance, reliability and maintainability; in addition toinsensitivity to generic failures.

In the patent literature, U.S. Pat. No. 4,443,853 to Maciolek et al.shows an electrically controlled mechanical actuator driven by opticallygenerated electrical power through an optically controlled switch in anelectrically isolated module. Maciolek et al. however, in contrast doesnot show the use of dual coil with diode control, nor opticallycontrolled dual switches, nor a power supply circuit for the dual solarcells, nor the dual servoamplifiers, nor the RS dual optical links asexemplified by embodiments of the present invention.

Further exemplary of the prior art is U.S. Pat. No. 4,132,278 to Stevenswhich relates to a control system for aircraft includingelectrohydraulic valve means, however in contrast to the presentinvention does not use optical means for power transfer, but useshydraulic power exclusively to produce electrical power.

SUMMARY OF THE INVENTION

The present invention uses either a conventional or modifiedelectrohydraulic (EH) servovalve with reduced electrical powerconsumption for the operation of the actuator. The EH valve of thepresent actuation system receives pulse width modulated electricalsignals to operate its first stage valve (torque motor). The pulse widthmodulated signals are created by an optically controlled switchingmechanism as for the valve saturation needed D.C. currents areinterrupted by pulse modulated switching mechanism. Constant D.C. powersupplies are provided as hereinafter described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a first embodiment of anoptoelectric/hydraulic servovalve with actuator in accordance with thepresent invention;

FIG. 2 is a schematic block diagram of a further embodiment of anoptoelectric/hydraulic servovalve with actuator in accordance with thepresent invention;

FIG. 3 is illustrative of the use of optically controlled dual-switchesin the present opto-electric/hydraulic servoactuation system of FIG. 1;and,

FIG. 4 is a schematic illustrative of the change in the system of FIG. 2utilized for the elimination of hardover in any direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The Problem

The biggest problem of a Fly-By-Light (FBL) actuation system is theoperation of the servovalve. The servovalve may receive fiber-opticsignals, but it needs some power for operation of first stage valvemechanism. At present, the photonic technology is not best source forprovision of power for safe and reliable valve operation to replaceelectrical power. External or internal electrical power supplies canprovide sufficient power for valve operation. The external power supplymay be affected by EMI and internal power supplies needs electric powergeneration.

When the requirement forbids external or internal electric powersupplies to the valve, the following solutions are tried with variablesuccess.

1. Laser diode signals are used to operate the mechanism of the firststage valve through heat provided by laser. This method was notsuccessful to produce valve operation with sufficient bandwidth requiredfor high performance aircraft, because the time requirements for heatingand cooling either metals, or liquids or gases.

2. More success can be achieved in combination of fiber-optic signalincsand fluidic amplification. The valve receives fiber-optic signals, whichcontrols the first stage of a fluidic amplifier. The speed of fluidicamplification is the main factor to determination of the valvebandwidth.

3. The signals from laser diodes are converted into electrical signalsfor the operation of servovalve. This type of operation is dependentupon the reliability of fiber-optic signaling in different environmentalconditions.

The present invention hereinafter described, provides a unique andpractical solution for the operation of an optic-electric/hydraulicservovalve and hydraulic actuation, with an emphasis on the reliabilityof valve operation in different environmental conditions.

Mechanization

The present system concept hereinafter described is dependent on thefollowing principles:

1. Pulse width modulated electrical signalings from a fiber-opticcontrolled electrical switch to the torque motor of an electrohydraulicservovalve.

2. Optical signalings from the controller to the switching mechanism.

3. Reliable electrical D.C. power source, which can be provided eitherthrough laser diode power source or batteries or solar cells or highintensity lamps. The constant D.C. power level has to be maintained.

All the components in accordance with the above system concept arecombined into one opto-electric/hydraulic valve unit and attached to thehydraulic actuator. This valve unit receives optical power and opticalcontrol signals from Actuator Control Electronics (ACE). Additionally,it receives fluid flow from hydraulic power supply for valve andactuator operation.

Two configurations of an opto-electric/hydraulic servovalve withactuator are shown in block diagram form in FIGS. 1 and 2. The twoconfigurations represent the same system concept, the difference is inredundancy management for improvement of reliability and safety.

The first as shown in FIG. 1, utilizes duplicate components andsignalings. It is designed so each coil of a dual-coil servovalve can beoperated by different fiberoptic/electric channel. The secondconfiguration utilizing the aforementioned system concepts with oneservovalve is shown in FIG. 2. FIG. 2 may be satisfactory in respect ofreliability and safety, but with reduced complexity weight and cost.

Electrohydraulic Servovalve

A regular or a modified electrohydraulic servovalve 22 (modified forreduced power consumption) receives pulse width modulated electricalsignals 24. The D.C. voltages of the signals are regulated by a powersupply circuit 26, and interrupted by optically controlled switch viaoptical link to the ACE.

Electrohydraulic servovalve 22, therefore, will receive electrical stepinputs (pulses) with voltages kept constant at valve saturation level.The time of the pulses are converted into differential pressure at thefirst stage valve of servovalve 22 and consequently into fluid flow bythe second stage valve. The flow from the second stage valve to actuator30 determines the actuator position and velocity.

Basically, electrohydraulic servovalve 22 receives step input signalsequivalent to voltage and current needed for valve flow saturation andthese pulses are time modulated for the required hydraulic flow and soactuator motions.

Switching Mechanism

The switching mechanism is designed to receive constant D.C. electricalinputs from power source 34, which is then pulse modulated byfiber-optic signal from the actuator controller. Therefore, the outputfrom the switching mechanism to the electrohydraulic servovalve will bepulse modulated step signals. These step signals will be amplified tothe saturation voltage level of the electrohydraulic servovalve orslightly higher.

Power Supply

The present opto-electric/hydraulic valve system needs two differenttype external power supplies, one optic and the other hydraulic.Additionally, it needs internal electrical power to operate the firststage valve of an electrohydraulic servovalve. This internal electricalpower supply has to be locally generated or supplied by optical means.

Power source 34 for opto-electric/hydraulic servovalve 22 can be a laserdiode/an LED/or hi-intensity lamp. Coupling efficiency of laser diodewith 100/140 micron fiber is the best. Laser diode power supply will becontrolled through an optical link by Actuator Control Electronics (ACE)40. ACE 40 will also activate switch optically to open or close thevalve by controlling D.C. voltage. Since laser diode is subject totemperature effects, stable power could become an issue. A powerconditioning circuit with regulator and filter may be built in theswitch.

Two methods for avoiding EHV hardover resulting from either failure inone switch operation or failure in one fiber path or in one photovoltaicdevice.

Method 1: Dualization switches (Fail-Passive Switching)

The system of FIG. 1 is modified as in FIG. 3 as each switch operationis dualized. As one switch or optical fiber path failed, the redundantswitch in series can cut off any hardover failures, and the EHV willfail passively, as the other ACE will recognize the failure and takescorrective steps. The windings of EHV coils are designed to providedifferent direction torques. The operation of switches is shown in thefollowing table:

    __________________________________________________________________________                                   CURRENT                   SWITCHES        AFTER SWITCHES    NORMAL OPERATION                   A   B   C   D   B     D    __________________________________________________________________________    Light from ACE 1                   Closed                       Open                           Open                               Closed                                   No    Current (+)    Light from ACE 2                   Open                       Closed                           Closed                               Closed                                   Current (-)                                         No    No Light from ACE 1 or Ace 2                   Open                       Closed                           Open                               Closed                                   No    No    FAILURE IN OPTICAL    FIBER PATH    Loss of Light From    ACE 1          Open                       Closed                           Open                               Closed                                   No    No    ACE 2          Open                       Closed                           Open                               Closed                                   No    No    __________________________________________________________________________

Method 2

With the change shown in FIG. 4, the circuit of the hardover in thesystem of FIG. 2 in any direction can be eliminated.

A power supply with RS232 link 101 and switch 103 can be commanded forpositive or negative voltage to be fed to Op-Amp 105; with Vin positive,diode 107, provides negative feed back; the output follow the input;coupled by the diode. For Vin negative Op-Amp 105 goes into negativesaturation, and Vout is at ground.

Use of software for implementation of switch 103 in the power supply canbe controlled for positive and negative voltages, hereby virtuallyeliminating the hardover problem in any specific direction.

Thus, although version aspects of the invention have been shown anddescribed with respect to exemplary embodiments thereof, it should beunderstood by those skilled in the art that the foregoing and variousother changes, omissions and additions may be made therein and thereto,without departing from the spirit and scope of the invention.

What is claimed is:
 1. A dual coil electrohydraulic servovalve whereineach coil of the electrohydraulic servovalve utilizes an opticallycontrolled switch and a redundant switch coupled in series therewith andupon failure of either optically controlled switch, said redundantswitch in series will cut off any hardover failures of said controlelectrohydraulic servovalve.
 2. A dual coil electrohydraulic servovalvewherein each coil of the electrohydraulic servovalve utilizes anoptically controlled switch and a redundant switch coupled in seriestherewith and upon failure of either optically controlled switch saidredundant switch will cause said dual coil electrohydraulic servovalveto fail passively.